Motor control system



June 14, 1932. L. c. HARDESTY 1,863,403

IOTOR CONTROL SYSTEI Filed Nov. 24, 1928 Inventor: L lewei lyn C. Hardestx y His Attor ney tors in i which the ar cuitthr'ou' h' a 4 i voltage red 'uein'g device and Patented June 14, 1932 UNITED I sTA-T s fj PATENT OFFICE LLEWELLYN c. nannas'mr. or :sco'rLa, nnw- YORK, ASSIGNOB To sensual. ELECTRIC 4 5COKPANY.1;AACORPORATIONI or maw YORK MOTOR CONTROL SYSTEM.

ap nejinbh alegtnove'inberjzl, ta es. .s er ial ll'o tlglfll fi My invention relates try-controllers for elem tric motors and more particularly to cont-rollers for starting'altcrnating current mothe motor is 'conuec teklto resistance or An object of my ni'entionistlic' pr o i'is ion" "of simple and starting deyicef "whereby the motor' may U started nd hrought up to itsrm'ining speed in a safe," reliable and etlieieut manner.

In a particular embodiment ot my' inven tion I employ a line"cout:ictbr'to startthe" 'motor by connecting the animals ofithe motor \vith'the line throng h'asuitahle re-l sistan'ee. and a f-unning :o!itaetor connected 'tohe energized iirz'ici-iii'elandefwith the eounter E. M. F. iii the "IimtorI to lshortcir euit the' resistance andi ivnnct tll'eittlqlitilf. (iiline after 'it; has colnefiipto" speed together with. 'a time elcnnent "ineans for preventing the operation of the running centaet'or for a definite time intervalafter' the operation of the line. eontactor.

A further ohjeetof the invention is to insure that the running eoutaetor will not elose'and short circuit the resi tanee and supply full line voltage to theteruiiuals until the motor has come upto :rprerletermined spee(l Further and ancillary ohjeets of the invention will manifest thel'nselves to those skilled in the'art from the tltltllltil description and explanation which follows.

For a hetter understanding of my 'invention refereuee should he had to the followin; specification tt-igether with the aeeompanying drawing, the single figure of which is a iliagramumtieal representation of an emhodiment of my invention Referring now to the drawing, I have shown my invention in one form as a iplii-(l to an alternating current motor 1" adapted to be connected with a souree of electric power which for the purposes of illustration l have shown as a three 'pha source represented lay the three supply lines 11. in order that full line voltage shall not be applied i nigemeiit is -such that .IS' 2 revie tot the-terminals ofthe motor during the start fing operation until the speed of the motor has; reached a predetermined val no, a. v voltagefrc(lueiugdeviee comprising the three rcthe suppl y cirsistorsj lil isprm'ided; A line contactor 13 otlierf su table sefregfivhen operated to closed position, to connect-1 the terminals of the motor 10 with the supply line "11 through the resistors 12.

Running connection between the motor 'fand the supply line inwhich the resistors lljare short clrcilited'aliil 'full line. voltage is ap hed to the terminals of the motor, is estab ished b the closing of "running con- "tactor 14. T e energizing coil 15 of the contaetor 14 is supplied from the terminals 17 and-18 of one phase. otthe motor 10 and this, (oil is so designed that. it will not close the running contactor 14 -until the terminal voltage"of'the motor has reached a reg'detcrihincdyalue," The energizing coil 19 "'of the line e'ontact'or 14 is adapt-ed to be conneetedfivith onephase' of thethree phase sourceiif supply 11 through the conductors 20am] 2). and the movable and stationary -eontacts'23fand '24 .ot the starting button.

Starting button 23; which I have shown as a push. hutton type of eontactor normally biased to the. open position by the spring 28 hut which may he. any suitable type of contact making device. is provided to hridge the stationary contacts 24 when depressed momentarily, and to energize the coil 19 and initiate the. starting operation. Auxiliary eontaets 25 on the eontaetor 13 are adapted to he bridged hy thehridging member 26 when the contactor 13'is moved to closed position-thereby toestahlish' a self-holding circuit for the energizing coil 19. A stop button 27 normally "biased to the closed position by the. spring 30 to bridge the stationary contact members 29 serves when tern po- 'rarilv depressed to open the circuit of the energi izing coil 19 to initiate the stopping operation.

Those skilled in the artwill understand that at the instant that the tips 31 of the line contaetor 13 engage the stationary contact members 32 and before the current through the resistors 12 has built up to an appreciable value,.full line voltage will be impressed upon the motor terminals. If energizing coil 15, which is set for a voltage lower than the full line voltage, were connected directly across the terminals of the motor at this instant when full line voltage exists at the motor terminals, running contactor 14 would be actuated to the closed position and the resistors 12 would be short clrcuited. In this condition an excessive voltage would be maintained at the motor terminals and an excessive current would be caused to flow in the windings until the mo tor accelerated suliiciently to reduce the current to normal value. This condition would be abusive of the apparatus and might even result in serious damage to the a paratus. To prevent such an occurrence, a de nite time delay device 33 is provided the function of which is to delay the energization of the coil 15 for a period of time after the operation of line contactor 13 to permit the current to build up in resistors 12 and reduce the voltage at the motor terminals to a value lower than that for which relay 15 is set to operate. Although any suitable type of time delay device may be used, I prefer to use the type shown in the drawing which is described and claimed in copendin application Serial No. 161,919 Robert \V. off, filed January 18, 1927. The coil 15 is connected across the terminals of the motor in a circuit that is normally open at the stationary contacts 36. A spring 34, which is placed under tension by the closing operation of contactor 13 sets the time delay device 33 into operation and causes the contactor 35 to bridge the contacts 36 at the expiration of a definite interval of time. After the closing of line contactor 13 suitable protection against overload is afforded by an overload protective device which is illustrated in the drawing as an overload tempera ture relay 37.

v The starting operation proceeds in an extremely simple and straight forward manner. As shown in the drawing the apparatus is in its normal or pre-starting position with both the line contactor and the running contactor in their open circuit positions. To start the motorthe button 23 is momentarily depressed to bridge the stationary contacts 24 and establish connections between energizing coil 19 and the source of supply over a circuit that may be traced from one side of the source of supply 11, conductor 22, energizing coil 19,

bridging member 23 and stationary contacts 24, bridging member 27 and stationary contacts 29 of the stopping button, conductor 38, contacts 39 of the overload temperature relay, conductor 43 to conductor 20 and an opposite side of the source of supply 11. Line contactor 13 now closes and connects the terminals of the motor 10 with the source of supply 11 through the voltage reducing resistors 12 over the following circuit: Conductors 20, 21, and 22, conductors 40, 41, and 42, resistors 12, conductors 50, 51, and 52, and terminals 16, 17, and 18 of the motor 10. llhose skilled in the art will understand that as a result of the closing of line contactor 13 that full line voltage will exist momentarily at the terminals of the motor 10. However, as the current builds up in the resistors 12 and the voltage drop across the resistors increases, the voltage at the motor terminals becomes reduced to a value considerably lower than the line voltage and the motor will be accelerated from rest to a speed that is proportional to the applied voltage. Contactor 13 in closing, causes bridging member 26 to bridge the auxiliary contacts 25 and short circuit the stationary contacts 24 of the startin button to establish a self-holding circuit or energizing coil19. In closing, contactor 13 also places spring 34 under tension and causes the time relay device 33 to actuate the movable contactor 35 in a counterclockwise direction and after a definite time interval to bridge the stationary contacts 36 thereby to establish a circuit for energizing coil 15 that extends from mot-or terminal 18 over conductor 44 through coil 15, conductor 45, stationary contacts 36, and contact 35, conductor 46, and conductor 51 to an opposite terminal 17 of the motor.

When the motor has accelerated sufliciently and its counter-voltage has built up to the value for which the coil 15 is set to operate, running contactor 14 will close its contacts short circuiting the resistors 12 a'nd connecting the motor terminals directly with the line. As a result of this operation full line voltage will be applied to the terminals of the motor 10 and it will be accelerated to full running speed. It will have been observed that at the instant that the tips of line contactor 13 were moved into engagement with the stationary contacts 32, the circuit of the energizing coil 15 was open at the contacts 36. And it will be understood that the current flowing through resistors 12 will have had suflicient opportunity tobuild up and reduce the voltage at the terminals of the motor 10 before the definite time delay device 33 has had sufficient time to complete its operation and cause the contacts 36 to bebridged and the energizing coil 15 to be connected to the motor terminals. Thus, it will be seen that running contactor 14 can not close its contacts until the motor has reached the speed for the corresponding voltage of which the energizing coil 15 is set to operate.

To stop the motor the stopping button 27 is momentarily depressed and the circuit of the energizing coil 19 is opened at the stationary contacts 29. As a result of this, all contactors open and the motor terminals are dis connected from the line. When line contactor 13 op'ens, the tension on the spring 34 is relieved and the time delay device 33 is returned to its pro-starting position with the contactor 35 out of engagement with the stationary contacts 36.

Although I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisons of the patent statutes, I would have it understood that I do not limit my invention thereto, for various modifications thereof will readily suggest themselves to those skilled in the art without departing from the spirit of my invention or the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination with an electric motor, a current limitin device, a line contactor, manually operated means for operating said line contactor to supply current to said motor through said current limiting device, a running contactor for short circnitin said our rent limiting device, means inclu ing a coil for responding to a predetermined counter' voltage of said motor to operate said running ,contactor, and a time delay device set in o ration responsively to the operation of said line contactor for connecting said coil to the terminals of said motor a predetermined interval of time after the operation of said line contactor. v

2. In combination with an electric motor, a starting device.for said motor comprising a resistance device, a line contactor for-com necting the terminals of said motor to a source of supply through said resistance device, operating means for said line contactor inc uding an electroresponsive device connected across the line in a normally open circuit and manually operated means for closing said normally open circuit, a running contactor for shortcircuiting said resistance device and means for operating said running contactor comprising a coil for responding to a predetermined motor voltage connected in a normally open circuit across the motor terminals, and a time delay device operable in response to operation of the line contactor for closing said last mentioned normally 0 n circuit a definite interval of time after t e operation of the line contactor.

In witness whereof, I have hereunto set my hand this 23rd da of November, 1928.

LLEWELL C. HARDESTY. 

